It is well known that olefins can be polymerized with complex catalyst compositions consisting of two or more independent components. For example, in the so-called Ziegler process a transition metal compound like TiCl.sub.3 is treated with an activating agent like aluminum alkyl and the resultant composition is used in ethylene polymerization. Recently in U.S. Pat. Nos. 3,488,333, 3,647,722 and 3,642,746 are described modifications whereby the transition metal compound is supported on a carrier like magnesium carbonate, magnesium chloride, etc. thus enabling higher reactivity. These catalysts are insoluble in hydrocarbon solvents and the chloride residue left in the polymer is harmful.
Another well known process is the Phillips process in which chromium oxide supported on silica is used after oxygen (air) activation. In U.S. Pat. Nos. 3,130,188 and 3,165,504 are described (NH.sub.4).sub.2 SiF.sub.6 and ZrF.sub.4 modifications of the basic CrO.sub.3 -silica catalyst system to increase the activity. One of the disadvantages of this system is the extreme susceptibility of the catalyst to damage by traces of oxygen, carbon monoxide, water, etc. Extreme care should be observed in the polymerization of this system. The CrO.sub.3 -silica catalyst system has another disadvantage of having an induction time which tends to cause operational problems in the manufacture of polyolefins such as polyethylene by this process.
In U.S. Pat. No. 3,622,521 there is described a modification of the chromium trioxide-silica catalyst by including tetraisopropyl titanate. The patentees found that a catalyst containing, for example, 5% titanium gives a higher melt index material.
In Pullukat et al U.S. Pat. No. 3,780,011 assigned to the same assignee as the present application there is described a catalyst containing titanium, for example 3.5% titanium, on chromium trioxide-silica to give higher activity, higher melt index, and higher HLMI/MI for the polymer and also no induction time in etylene polymerization.
Recently a different type of olefin polymerization catalyst has been described. In U.S. Pat. Nos. 3,324,101, 3,324,095 and 3,468,865 are described catalyst systems consisting of an organosilyl chromate and an aluminum alkyl deposited on silica.
In U.S. Pat. No. 3,493,554 is described a bis(diorgano) chromate-aluminum alkyl system. These catalysts even though they do not contain chlorides have the disadvantage of being relatively unstable. In fact, some silyl chromates are known to explode violently.